Multiple feed point slot antenna

ABSTRACT

A wireless communication device and method for identifying a container, or communication information about a container using a slot in the container as an antenna. The device includes a wireless communication device for transmitting information regarding the container. The container includes an outer wall forming rim and a slot between the rim edge and the outer wall that is circular and continues without boundaries. The wireless communication device is coupled to the slot to provide the slot antenna for communications. An impedance matching network is additionally provided to make the operating frequency of the slot substantially the same as the operating frequency of the wireless communication device. Alternatively, shorting posts may be placed in the slot to define boundaries of the slot to match the operating frequency of the slot to the operating frequency of the antenna. Multiple feed points may be provided between the wireless communication device and the slot.

RELATED APPLICATIONS

The present application is a continuation-in-part of application Ser.No. 09/536,334 filed Mar. 25, 2000, entitled “Remote communication usingslot antenna”.

FIELD OF THE INVENTION

The present invention relates generally to a device and method foridentifying a device or article of manufacture such as a container and,more particularly, to a device and method using the slot of thecontainer as an antenna for remote communications.

BACKGROUND OF THE INVENTION

It is often necessary to monitor the location and movement of materialswithin a distribution center or manufacturing facility. One method oftracking the materials is to attach a wireless communication device,such as a radio frequency identification (RFID) transponder or otheridentification device, to an article of manufacture including any typeof physical device or container that houses materials. This applicationrefers to this physical device or article of manufacture as a containerfor brevity sake only.

By way of example, a liquid container such as a barrel or keg mayinclude an identification device indicative of the liquid containedinside. A transmission device, such as an interrogation reader ortransmitter, having an antenna device, is able to send informationremotely through electronic signals. Such transmission device is placedthroughout the distribution or manufacturing facility to receive signalstransmitted from wireless communication devices. The signals are thenpassed to a central control system that monitors and records theapplicable information. The central control system can also sendinformation to its interrogation readers to send to the transponders forresponse and/or to be stored in the transponder's memory.

The information communicated by the containers in the system to theinterrogation readers may be used for a number of reasons. For example,a statistical analysis may be made of the materials to maintain anaccurate inventories, production flow rates, and other productionstandards. Additionally, the identification devices may include specificinformation about the materials housed within the containers, includingdate of manufacture, place of manufacture, type of product within thecontainer, temperature of the container and ambient air, temperature ofthe contents of the container, pressure of the container, etc.

The wireless communication device must have some type of antennaarrangement to communicate information about the containers to theinterrogation readers. It is generally known for wireless communicationdevices to include an antenna. It is often a problem for many wirelesscommunication devices to provide antennas, especially if the wirelesscommunication device is small or is required to be placed in a containedarea. The length of the antenna must be tailored to the specificfrequency at which the wireless communication device is designed tooperate. For low frequencies in the MHz range or lower, an antenna mayhave to be several inches long to several feet long. The antenna mayhave to be several inches long for higher frequencies, to allow forsuccessful communication at the desired operating frequency.

Additionally, the antenna must either be packaged inside the wirelesscommunication packaging that houses the wireless communication device,or located external to the wireless communication device. Externalpositioning of the antenna to the wireless communication device providesseveral other challenges when placing the wireless communication devicein a confined area, such as in a container. The antenna may haveadditional problems radiating energy effectively if the antenna iscontained internal to a device, such as a container.

A beer keg is one example of a container that one may wish to attach awireless communication device. A beer keg has a substantiallycylindrical shape with a smooth, uniform outer wall. There are noextensions or areas for effectively attaching the wireless communicationdevice. Even if the wireless communication device can be attached to thekeg, additional problems in packaging and unaltered communication existswhen including an antenna for the wireless communication device asdescribed above.

Some containers have a natural slot as a characteristic of theirmanufacture. A slot may be formed by edges of a conductive materialcoming together in close proximity forming a gap of air between theedges. A slot may also be formed by cutting out or removing materialfrom a conductive surface to form an open or hollow area of free spaceor air. A slot could be formed by a curl of a cylinder or other surfaceto form a rim, whereby a slot is created by the gap between the end ofthe curl and the surface.

For example, a beer keg is made out of a metal material that has anouter wall with a curled end to form a rim. The keg rim is used forhandling and movement of the keg. The curled portion of the rim bendsinward towards the outer wall, leaving a small gap between the edge ofthe rim and outer wall. This small gap forms a slot that extendscircularly around the keg, and can be used to provide a slot antenna forthe wireless communication device. The wireless communication device canbe designed to provide electronic connectivity to the slot wheninstalled, so that the slot can be used to provide the effect of anantenna. Since the slot of the container may be several feet long, usingthe slot for the antenna may be advantageous for communication at lowerfrequencies where providing an antenna of sufficient length forcommunication at the desired frequency is problematic.

Therefore, it is advantageous to use the slot of a container to providean effective antenna for a wireless communication device. In the parentapplication of the present invention, use of the slot was explored atlength. However, it has been discovered that there may be occasions whenit is desirable to change the radiation pattern of the slot antenna suchthat it has better omni-directional receive and transmit capabilities.Further, there may, on occasions, be a need to change the operatingfrequency of the slot antenna such that the wireless communicationdevices operates at multiple frequencies.

SUMMARY OF THE INVENTION

The present invention includes a wireless communication device using aslot antenna arrangement formed by the slot of a container. A wirelesscommunication device is provided with the container to provideinformation about the identification or other aspects of the containeras it moves through manufacturing, tracking or shipping facilities.

An antenna is provided for the wireless communication device so that itcan communicate remotely with a transmitter/receiver. The presentinvention capitalizes on the phenomenon that exists whereby a slot in aconductive material, such as metal, aluminum, copper, or iron forinstance, can be coupled to a wireless communication device'scommunications electronics to provide the effect of a pole antenna.

Some containers have by the nature of their construction a slot that canbe used to provide a slot antenna. Alternatively, a slot can also be cutout of the container as well. Using a slot antenna instead of a poleantenna provides several advantages. The required length of the slot forthe wireless communication device to operate at the desired frequencymay be more easily implemented than could be provided by using a poleantenna. Additionally, the slot does not require that a pole device beplaced inside or proximate to the container. This is especially helpfulfor lower frequency communications that require longer length antennas.Using the slot may also be less expensive than using a pole antenna.Additionally, a pole antenna may extend from the container therebyexposing the pole antenna to damage.

In one embodiment, the wireless communication device uses feed linesdirectly connected to the each edge of the slot.

In another embodiment, the wireless communication device includes feedlines that reactively couple with each edge of the slot.

In another embodiment, a conductive device is placed between the slot tocouple the wireless communication device to the slot and provide theslot antenna.

In yet another embodiment, the wireless communication device is mountedon a non-conductive substrate in the slot. A feed line from the wirelesscommunication device rests on the substrate such that it reactivelycouples with the slot to provide the slot antenna.

A technique is provided to ensure that the operating frequency of theslot matches the operating frequency of the wireless communicationdevice to maximize the slot antenna radiation efficiency. A circuit isprovided in between the slot and the wireless communication device tomatch the impedance of the slot to the impedance of the wirelesscommunication device.

In an alternate embodiment, shorting posts are provided on the ends ofthe slot to create a slot with the desired length. The shorting postsare constructed out of a conductive material, such as metal, aluminum,copper or iron for example, and are placed between the slot's edges toshort both sides of the slot together.

The present invention also provides a technique to improve theomni-directional transmission and reception capabilities of the slotantenna. In particular, multiple feed lines may be used at variouspoints around the slot, thereby increasing the ability of the slotantenna to radiate and receive electromagnetic signals. The multiplefeed points may be positioned such that reflections occurring on theantenna are cancelled. The multiple feed points may alternatively bepositioned such that antennas with different operating frequencies areformed thereby.

Within this concept are multiple embodiments. In particular, there may asingle radio frequency transmission line with multiple feed pointsconnecting the transmission line to the slot antenna with one rectifierin the transmission line. In an alternate embodiment, there may be atransmission line with multiple feed points connecting the transmissionline to the slot antenna with one rectifier per feed point. In stillanother alternate embodiment, multiple transmission lines may be used,each terminating with a feed point, connecting the transmission line tothe slot antenna. In yet another alternate embodiment, the positions ofthe feed points are such that the slot antenna actually forms aplurality of antennas, each adapted to receive and transmit optimallydifferent frequencies. It should be further appreciated that the type oftransmission line may be varied, and suitable options include coaxialcable, insulated wires, micro-strip style transmission lines, or thelike as needed or desired.

The invention also includes a method of monitoring the container. Whilethe container is within a facility, such as during manufacturing,filling, or storing, the container is moved through at least oneinterrogation point containing an interrogation reader. Communicationbetween the wireless communication device and the interrogation readeris established for monitoring the location and/or content informationabout the container. A central control system may be in communicationwith the interrogation point for monitoring the movement of thecontainer. The central control system may monitor the position of thecontainer, or it may also monitor specific information that is storedwithin memory in the device, or both.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one type of container, known as a keg,constructed in accordance with the present invention;

FIG. 2 is a cross sectional side view of the slot in the container;

FIG. 3 is a schematic diagram illustrating communication between thetransponder and an interrogation reader;

FIG. 4A is a schematic view of the slot antenna using direct feed lines;

FIG. 4B is a schematic view of the slot antenna using reactive feedlines;

FIG. 4C is a schematic view of the slot antenna using a transpondermounting device as feed lines;

FIG. 4D is a schematic view of the slot antenna using feed lines on anon-conductive substrate to couple to the slot;

FIG. 5 is a schematic diagram illustrating the radiation pattern of theslot antenna arrangement;

FIG. 6 is a schematic diagram of an impedance matching circuit betweenthe slot antenna and the transponder;

FIG. 7A is a schematic diagram of the slot antenna using shorting poststo create a monopole antenna equivalent;

FIG. 7B is a schematic diagram of a typical monopole antenna radiationpattern;

FIG. 8A is a schematic diagram of the slot antenna using shorting postswith the transponder in between the shorting posts to create a dipoleantenna equivalent;

FIG. 8B is a schematic diagram of a typical dipole antenna radiationpattern;

FIG. 9 is a top plan view of a container with multiple feed points;

FIG. 10 is a partial cross-sectional view along lines 11—11 of FIG. 9;

FIG. 11 is a top plan view of an alternate embodiment of a containerwith multiple feed points;

FIG. 12 is a top plan view of an alternate embodiment of a containerwith multiple feed points and multiple feed lines;

FIG. 13 is a schematic diagram of a micro-strip transmission lineembodiment; and

FIG. 14 is a schematic diagram illustrating the tracking and informationsystem to track containers having a transponder.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a device and method of using a slotin a container as an antenna for a wireless communication device. Asillustrated in FIGS. 1 and 2, the invention includes a wirelessidentification device 30, called a “transponder,” that is mounted in acontainer 10 for identifying the container 10. The container 10 hasouter walls 12, including a bottom wall 18, a top wall 19, and outerwalls 12 sealed together forming an enclosed chamber for housing amaterial 16. A rim 14 is formed by the outer wall 12 and may extendabove the top wall 19 and the bottom wall 18, for handling the container10. The outer wall 12 extends upward and curls inward to form the rim14. The gap between the end of the curled outer wall and the outer wall12 is called the slot 20 that extends around the circumference of thecontainer 10. A transponder 30 is provided within the rim 14. Thetransponder 30 may contain information about the container 10 that iscommunicated to at least one interrogation reader. It should be readilyunderstood to one of ordinary skill in the art that the presentinvention is not limited to the particular container 10 illustrated inFIGS. 1 and 2, and that the present invention is applicable to othertypes of containers having a slot 20.

FIG. 3 illustrates one particular type of wireless communication device30 called a radio frequency transponder 30. This application uses atransponder 30 to describe the present invention, but transponder 30 andwireless communication device 30 are equivalent devices that can be usedinterchangeably with the present invention. It should be readilyunderstood to one of ordinary skill in the art that there are many otherdifferent types of wireless communication devices that allow electroniccommunication. The present invention is described as using a transponder30 as the wireless communication device as these terms areinterchangeable. The present invention is not limited to any oneparticular type of wireless communication device 30, including atransponder 30.

The transponder 30 includes a control system 34 and wirelesscommunication electronics 32. The transponder 30 may also contain localmemory 36 for storage of information to be communicated to aninterrogation reader 40. Alternatively, the transponder 30 may storeinformation, such as an identification number or indicia, by usingdiodes, dip switches, or some other like circuitry. However, the presentinvention is not limited to transponders 30 that contain memory 36. Anantenna 38 is also provided for communications that may be eitherexternal to or incorporated internal to the transponder 30. Theparticular type and location of the antenna 38 will depend on theoperating frequency of the transponder 30 and the particular designdesired.

The control system 34 is an integrated circuit or other type ofmicroprocessor or microcontroller electronics that controls thesubstantive operations of the transponder 30. The control system 34 isconnected to the wireless communication electronics 32 to communicateand receive transmissions. The control system 34 is also connected tomemory 36 for storing and retrieving information. Control system 34 mayfurther include a clock.

FIG. 3 also depicts how communication is achieved with the transponder30. An interrogation reader 40 contains interrogation communicationelectronics 42 and an interrogation antenna 44. The interrogation reader40 communicates to the transponder 30 by emitting an electronic signalor command 46 modulated in a frequency through the interrogation antenna44. The interrogation antenna 44 may be any type of antenna that canradiate the modulated signal 46 through a field 48 so that a compatibledevice, such as the transponder 30, can receive such signal 46 throughits own antenna 38. The field 48 could be any of a variety of differenttypes used in electronic communications including electromagnetic,magnetic, or electric. The signal 46 is a message containing informationand/or specific instructions for the transponder 30.

When the transponder antenna 38 is in the presence of the field 48emitted by the interrogation reader antenna 44, the wirelesscommunication electronics 32 are energized thereby energizing thetransponder 30. The transponder 30 remains energized so long as itsantenna 38 is in the field 48 of the interrogation reader 40. Thewireless communication electronics 32 demodulates the signal 46 and sendthe message containing information and/or specific instructions to thecontrol system 34 for appropriate actions. For example, the request inthe message may be for the transponder 30 to communicate itsidentification information about the container 10 or the materials 16housed within the container 10 including, but not limited to, date ofmanufacture, place of manufacture, and type of product within thecontainer 10. The message may also be instructions to send backinformation regarding the temperature of the container 10, pressurelevels, etc. The transponder 30 communicates back the informationrequested to the interrogation reader 40 by altering the contents of thesignal 46 for whatever type of information is requested.

Alternative forms exist for communicating with a transponder 30, orother wireless electronic device. For instance, the transponder 30 mayhave a transmitter that can send information to the interrogation reader40 without having to alter the content of the signal 46. The transponder30 may contain its own power source, such as a battery, or other energystorage unit charged when the transponder 30 is in the field 48, topower the transmitter. It is understood to one of ordinary skill in theart there are many other manners in which to communicate with a wirelesscommunication device, such as a transponder 30, and that the presentinvention is not limited to the particular manner described above.

FIGS. 4A-4D show various configurations of slot antenna arrangements toprovide an antenna 38 by using the slot 20 in the container 10 aspreviously described. A slot 20 can provide a slot antenna 38 to thetransponder 30 by coupling the transponder to the slot 20. Moreinformation on slot antennas 38 and their operation is described in U.S.Pat. No. 4,975,711, entitled “Slot antenna device for portableradiophone,” incorporated hereby by reference in its entirety.

Voltage signals are provided by the transponder 30 to opposites sides ofthe slot 20. In the preferred embodiment for a beer keg container 10embodiment, one side of the slot 20 is formed by the outer wall 12, andthe other side of the slot 20 is formed by the rim edge 52. When thevoltage signals are applied across the slot 20, the slot 20 radiateselectro-magnetic waves similar to the manner in which a pole antennaarrangement would radiate to effectuate communications.

FIG. 4A illustrates a close-up view of the outer wall 12 and the rim 14illustrating how the transponder 30 uses the slot 20 as an antenna 38using feed lines 54 to form a slot antenna 38. The transponder 30 islocated in the inner portion of the rim 14. The slot 20 is formed by thegap between the outer wall edge 50 and the rim edge 52 that extendsaround the entire circumference of the container 10. Feed lines 54 areconnected to the outer wall edge 50 and the rim edge 52 to provide anelectrical connection between the transponder 30, particularly thewireless communication electronics 32, and the slot 20.

FIG. 4B contains an embodiment whereby the feed line 54 from thetransponder 30 does not directly connect to the outer wall edge 50 orthe rim edge 52. Instead, the feed line 54 is placed in close proximityto the outer wall edge 50 or the rim edge 52 to reactively couple to theslot 20. The feed line 54 is still excited without direct contactbetween the feed line 54 and the slot 20 due to its close proximity tothe slot 20.

FIG. 4C illustrates an embodiment whereby a mounting device containingthe transponder 30 is placed in the slot 20 to form the slot antenna 38,sometimes referred to as a conductive clip 60. A conductive clip 60, asused herein, is a device constructed out of a conductive material, suchas metal, aluminum, copper, or iron for example. The conductive clip 60keeps its form in a resilient manner, and can be inserted into a gap orspace in a secure manner. The conductive clip 60 provides both amounting technique for the transponder 30 and a connection between thewireless communication electronics 32 and the slot 20, to provide theslot antenna 38. The conductive clip 60 is substantially in the shape ofan “R”; however, other types of clips with the same characteristics asdescribed herein, may also be used. The transponder 30 is mounted to thetop of the conductive clip 60. The conductive clip 60 is inserted withthe round portion inside the slot 20 to provide a secure fit between theouter wall 12 and the rim edge 52. The portion of the conductive clip 60contacting the outer wall 12 provides a ground plane 62 for the slotantenna 38. The portion of the conductive clip 60 contacting the rimedge 52 provides a connection or feed line 54 to the slot 20 to providea slot antenna 38 for the transponder 30.

FIG. 4D shows another alternative arrangement whereby the transponder 30is mounted to a substrate material 70. The substrate material 70 is adielectric material. The substrate material 70 is curled and placedinside the rim 14. One side of the substrate material 70 contacts theouter wall 12, and the other side of the substrate material 70 contactsthe rim edge 52. The transponder 30 has a feed line 54 that extends fromthe wireless communication electronics 32 and rests on the substratematerial 70, extending downward proximate to the rim edge 52. Thetransponder 30, located proximate to the outer wall 12, providescoupling to the outer wall creating a ground plane 62 with earth. Thefeed line 54 extends to the rim edge 52 and is coupled with the rim edge52, either as an open circuit or a short circuit, to provide the optimumcoupling of the transponder 30 to the slot 20 to create the slot antenna38, depending on the length of the feed line 54.

FIG. 5 illustrates the radiation pattern of a slot antenna 38. Asillustrated under theoretical conditions, the slot antenna 38 radiationpattern is similar to a pole antenna arrangement, such as a dipoleantenna, but the E and H fields are interchanged. The actual radiationpattern of the slot antenna 38 in the present invention is a modifiedversion of this radiation pattern, due to both the curved nature of theslot 20 and the reflection from the surface of the container 10.Therefore, while it is noted that the radiation of the slot antenna 39may have the characteristics of that illustrated in FIG. 5, such isprovided for background purposes only. The present invention is notlimited to a slot antenna 38 with such radiation pattern.

When using a slot antenna 38, it is desired for the impedance of theslot 20 to match the impedance of the transponder 30 at the desiredfrequency to maximize energy transfer from the transponder 30 to theslot antenna 38. Such maximization of energy transfer allows thetransponder 30 to emit a maximum radiation pattern. Maximum energytransfer occurs when the impedance of the transponder 30 is theconjugate of the slot 20 impedance. If the transponder 30 has acharacteristic impedance that is not the conjugate of the slot 20, amatching network can be provided to do so. An antenna itself can beconsidered a matching network of sorts, transforming its terminalimpedance to 377 ohms, the impedance of free space. However, theimpedance of the transponder 30 may not be the same as the slot 20. Inthis instance, the slot antenna 38 may not perform optimally since themaximum energy transfer would not occur between the transponder 30 andthe slot antenna 38.

The slot 20 of the present invention has a fairly low impedance.Therefore, it may be necessary to transform the slot 20 impedance intothe impedance of transponder 30 to maximum energy transfer and thereforemaximize the strength of the radiation pattern emitted by the slotantenna 38. An impedance matching network, as illustrated in FIG. 8, isprovided to match the impedance of the slot 20 to the impedance of thetransponder 30 to ensure that the slot antenna 38 radiates an efficientradiation pattern for the operating frequency of the transponder 30 withminimal or no reflection. The matching network circuit converts theimpedance of the slot 20 to the impedance of the transponder 30 for anoperating frequency of 868 MHz. The transponder 30 has an impedance of50 ohms. The matching network circuit is connected on the rim 14 and theouter wall 12 across the slot 20 in parallel with a capacitor 120 ofapproximately 3 pF. The capacitor 120 is connected in series to aninductor 122 of approximately 5 nH. Another capacitor 124, ofapproximately 9 pF, is connected in series on the other side of theinductor 122. The capacitor 124 is connected to the wirelesscommunication electronics 32. It should be noted that thecharacteristics of containers 10 and slot 20 impedances for desiredfrequencies may require different matching networks than describedherein. The present invention is not limited to the particular impedancematching network illustrated in FIG. 6.

In this exemplary embodiment, the container 10 has a continuous slot 20that extends in a circular path. It may be desired to provide atechnique or manner in which to define the length of the slot 20 so thatthe slot antenna 38 radiates in an improved manner at the operatingfrequency of the transponder 30. One method of defining the slot 20length is to provide shorting posts 82 as illustrated in FIGS. 7A and 8Ato further improve performance of the slot antenna 38 depending on thefrequency. The length of antenna or the slot 20 for a slot antenna 38 isrelated to the radiation pattern of electronic signals radiated at thedesired frequencies. For instance, the length of a dipole antenna is λdivided by 2 where λ is equal to the speed of light divided by thedesired operating frequency, or equivalently, the wavelength. The lengthof the slot 20 is defined by the boundaries at which there is no longera gap of space or the placement of conductive material. Some slotantennas 38 are designed in containers 10 or other materials in whichthe slot 20 is placed at a predefined and desired length. The slot 20length is defined by providing a conductive material in the slot 20 thatshorts one side of the slot 20 to the other side. In the preferredembodiment, this is the outer wall 12 and the rim edge 52. Shorting theslot 20 gives a finite length to the slot antenna 38. Shorting posts 82are placed in the slot 20 at desired locations on each side of thelocation of transponder 30 coupled to the slot 20 to define the lengthof the slot 20. An impedance matching network may or may not benecessary with shorting posts 82, depending on if the impedance of theslot 20 and the impedance of the transponder 30 are matched sufficientlyin order for the slot antenna 38 to emit a desired radiation pattern.

FIG. 7A illustrates an arrangement where one shorting post 82 is locatednear to or proximate to the transponder 30 and the other shorting post82 is located a distance away from the transponder 30. The transponder30 is mounted to a carrier material 80 that is placed inside the rim 14for mounting the transponder 30 and shorting posts 82. The carriermaterial 80 is used as a convenient manner in which to mount thetransponder 30 and the shorting posts 82 in the rim 14 of the container10. The carrier material 80 is made out of a non-conductive material sothat it does not conduct with the slot 20, i.e. the outer wall 12 or therim edge 52. The transponder 30 is coupled to the slot 20 to provideslot antenna 38 by techniques of coupling the transponder's 30 wirelesscommunication electronics 32 as previously described above. Coupling thetransponder 30 to the slot 20 at or proximate to one of the shortingposts 82 creates a slot antenna 38 similar to a radiation pattern ofmonopole antenna like that shown in FIG. 7B, but it should be noted thatthe exact radiation pattern of the slot antenna 38 may be differentdepending on the frequency of the transponder 30 and the shape and othercharacteristics of the container 10.

Alternatively, as illustrated in FIG. 8A, the transponder 30 andshorting posts 82 are mounted on the carrier material 80 to mount insidethe rim 14 of the container 10 similar to FIG. 7A. However, thetransponder 30 is coupled to the slot 20 between the two shorting posts82. Coupling the transponder 30 to the slot 20 in the middle or centerof the shorting posts 82 creates a slot antenna 38 similar to a dipolelike shown in FIG. 8B, but it should be noted that the exact radiationpattern of the slot antenna 38 may be different depending on thefrequency of the transponder 30 and the shape and other characteristicsof the container 10.

In addition to changing the length of the slot antenna 38 through theuse of shorting posts, there may be occasions when it is desirable tochange the number and location of feed lines 54 thereby changing theradiation pattern of the slot antenna 38. In particular, theintroduction of additional feed lines 54 may allow the slot antenna toreceive and reflect incident radiation from any angle around thecontainer 10.

As illustrated in FIGS. 9 and 10, a conductor 200 may be positioned inloop 202 (FIG. 10) formed by rim 14 and particularly rim edge 52 andouter wall 12. A plurality of feed lines 54 electrically couple theconductor 200 to the slot 20. Conductor 200 is also electricallyconnected to the transponder 30. Conductor 200 may be any radiofrequency transmission line, such as a coaxial cable, a twisted pair, amicro-strip or the like. Multiple feed points 54 are provided betweenthe slot 20 and the transponder 30. Feed points 54 are points on theslot 20 that are connected to the transponder 30. It should beappreciated that the plurality of feed points 54 may be positioned, suchthat reflections between different feed points 54 and the transponder 30cancel. This occurs, as is well understood in the transmission line art,when the length between the points is an odd integer multiple of ¼wavelength of the operating frequency. Note also that the number of feedpoints 54 may be varied as needed or desired to achieve an optimalreflection pattern.

In FIG. 10, the feed points 54 may also provide additionallyfunctionality for mounting purposes, such as in the form of as springclips that hold the conductor 200 in place. It should be appreciatedthat nonconductive spring clips may be used to hold the conductor 200 inplace. In this manner, the feed points 54 serve only as an electricalconnection between the conductor 200 and the slot 20.

It should be appreciated that the number and positioning of the feedpoints 54 makes effectively a plurality of antennas for the transponder30, each potentially operative at a different frequency. Thus, theentire slot 20, would be a first operative antenna. The slot between anygiven feed point 54 and the transponder 30 would form another antenna,at a different frequency. It is possible that, dependent on the anglefrom which the incident radiation is received, cancellation of thesignal received from two of these different antennas may occur,resulting an effective null. However, as the container 10 is expected tobe moving through the field 48 of the interrogation reader 40, theantennas will also move within the field 48, and the null will beeliminated.

FIG. 11 shows an alternate embodiment of sing multiple feed points. Inparticular, a rectifier 210 may be associated with each feed point 54.In the previous embodiment, there was only one rectifier 210, and it wasincorporated into the transponder 30. In the present embodiment, eachfeed point 54 includes its own rectifier 210. In this manner, nulls areeliminated as each rectifier 210 produces a DC voltage and detects AMmodulation of the incoming radio frequency signal. Altering the DC loadfrom the transponder 30 may change the impedance of the rectifiers 210,causing a modulated reflection to send data back to the interrogationreader 40. A DC line 212 connected to the transponder 30 mayinterconnect the rectifiers 210, providing power and data communicationsat any angle. The DC line 212 may be a conductor buried in plastic orthe like, as needed or desired. As the antennas are not connected atradio frequencies, they do not interact in DC line 212, therebypreventing nulls in the receive pattern. The rectifiers 210 may also beconnected to multiple feed points that are matched to slot antennas 38operating at different frequencies, giving the multi-frequencycapability discussed above.

Another alternate embodiment is illustrated in FIG. 12, wherein multipleconductors 200, 222, 224 and 226 are used to connect the transponder 30to a number of feed points 54, in place of the single conductor 202 ofFIGS. 10 and 11. These conductors 220, 222, 224, and 226 may be anyconventional conductor, such as coaxial cable, twisted pairs,micro-strips, or the like, as needed or desired. Where wires are used,they may be bundled to conserve space. Again, the number and placementof the feed points 54 may be varied to change the operative frequencies,change likely destructive interference or the like as needed or desired.

FIG. 13 illustrates yet another alternate embodiment of the presentinvention. Using a micro-strip transmission line is especially wellsuited for this embodiment. An example of a micro-strip transmissionline is contained in U.S. Pat. No. 6,023,244 entitled “Microstripantenna having a metal frame for control of an antenna lobe,”incorporated herein by reference in its entirety. A micro-striptransmission line consists a piece of thin dielectric substrate thatcontains electronic components mounted in front of a ground plane,reducing mass production cost and product weight. In particular, thepresent embodiment incorporates electronic components into thetransmission line 228. Thus, for example, the transmission line 228 mayinclude feed points 54 and filters 230, 232. This may be accomplished bystubs with open or short circuits, narrowing or widening the micro-striptransmission line, or other appropriate technique as is well understoodin the transmission line art. Aside from filters, other electroniccomponents may also be performed using the transmission line 228. Forexample, impedance matching, couplers, splitters, and the like, may allbe facilitated through the present embodiment.

FIG. 14 illustrates a tracking system in which containers 10 containingtransponders 30 can be tracked through an environment such as a factoryor distribution facility. For example, the transponder 30 connected tocontainer 10 could pass a first interrogation point 90 that includes aninterrogation reader 40. When the container 10 and its transponder 30 isin the presence of the interrogation reader 40 as described previously,a message containing information and/or a specific request forinformation may be transmitted by the interrogation reader 40 andreceived by the transponder 30. This process continues as the container10 moves to a second interrogation point 92, a third interrogation point94, a fourth interrogation point 96, and on to a last interrogationpoint 98.

A central control system 100 maintains the information from theinterrogation readers 40 and monitors the movement of the containers 10through the facility. The information received by each of theinterrogation readers 40 may be forwarded to the central control system100 either through direct wire or LAN connection. The central controlsystem 100 could also send information to the interrogation reader 40 tobe transmitted to the transponder 30 for identification purposes. Thecentral control system 100 tracks the expected location of thecontainers 10 and may be alerted if it expects to receive informationabout a particular container and does not.

During commissioning of each container 10, it may be necessary to placethe container 10 containing the transponder 30 in range of aninterrogation reader 40 in order to erase previously stored informationin memory 36 or to store particular data or configuration informationabout the container 10 in memory 36 for later use.

In the foregoing description, like-reference characters designate likeor corresponding parts throughout the several views. Certainmodifications and improvements will occur to those skilled in the artupon a reading of the foregoing description. It should be understoodthat the present invention is not limited to any particular type ofcontainer or slot arrangement. One of ordinary skill in the art willrecognize that there are different manners in which containers withslots can be used to provide antenna functionality for a wirelesscommunication device in accordance with the present invention. It shouldbe understood that all such modifications and improvements have beendeleted herein for the sake of conciseness and readability but areproperly within the scope of the following claims.

1. A device for identifying a container having a slot, comprising: awireless communication device mounted on the container to communicateinformation associated with the container wirelessly; and a slot antennaformed by electronically associating said wireless communication deviceto the slot, said slot antenna including a plurality of feed pointscoupling said wireless communication device to said slot.
 2. The deviceof claim 1 further comprising a transmission line electricallyconnecting said wireless communication device to said plurality of feedpoints.
 3. The device of claim 1 further comprising a plurality oftransmission lines, each of said plurality of transmission lineselectrically connecting different ones of said plurality of feed pointsto said wireless communication device.
 4. The device of claim 2 whereinsaid transmission line is a coaxial cable.
 5. The device of claim 2wherein said transmission line is a twisted pair.
 6. The device of claim2 wherein said transmission line is a micro-strip transmission line. 7.The device of claim 1 wherein each of said plurality of feed pointsincludes a rectifier.
 8. The device of claim 1 wherein said plurality offeed points are positioned such that reflections between different onesof said plurality of feed points and said wireless communication devicecancel.
 9. The device of claim 1 wherein said plurality of feed pointsenables multi-frequency reception by said wireless communication device.10. The device of claim 1 further including a micro-strip transmissionline electrically connecting said plurality of feed points to saidwireless communication device.
 11. The device of claim 10 wherein saidmicro-strip transmission line includes at least one electronic componentincorporated thereinto.
 12. A system for identifying a container,comprising: a container having a slot; a wireless communication devicemounted on the container to remotely communicate information associatedwith the container; a slot antenna formed by electronically associatingsaid wireless communication device to said slot said slot antennaincluding a plurality of feed points coupling said wirelesscommunication device to said slot.
 13. A method of using a slot on acontainer as an antenna, comprising: associating a wirelesscommunication device with the container; positioning a plurality of feedpoints within the slot and electrically connected to said wirelesscommunication device; and communicating monitoring informationassociated with the container between said wireless communication deviceand an interrogation reader through a slot antenna formed by the slotwithin the container.
 14. The method of claim 13 further comprisinginterrogating said wireless communication device at a plurality offrequencies.
 15. The method of claim 13 further comprising positioning atransmission line proximate said slot to connect electrically each ofsaid plurality of feed points with said wireless communication device.16. The method of claim 15 further comprising integrating electroniccomponents on said transmission line.
 17. A container, comprising: aslot formed by a rim in the container; a wireless communication devicepositioned contiguous to said rim; a transmission line electricallyconnected to said wireless communication device; and a plurality of feedpoints electrically connecting said transmission line at differentpoints to said slot such that said slot operates as a slot antenna. 18.The container of claim 17 wherein said slot antenna operates at aplurality of frequencies.
 19. The container of claim 17 whereinreflections between said wireless communication device and each of saidplurality of feed points cancel.
 20. The container of claim 17 whereinsaid transmission line is held within said rim by a spring clip.
 21. Thecontainer of claim 17 wherein said transmission line is a coaxial cable.22. The container of claim 17 wherein said transmission line is amicro-strip transmission line.
 23. The container of claim 22 whereinsaid micro-strip transmission line includes at least one electroniccomponent integrated thereinto.
 24. The container of claim 23 whereinsaid at least one electronic component comprises an impedance matchingnetwork.
 25. The container of claim 23 wherein said at least oneelectronic component comprises a filter.
 26. The container of claim 23wherein said at least one electronic component comprises a coupler. 27.The container of claim 17 further comprising at least one rectifier,said rectifier operatively connected to said transmission line.
 28. Thecontainer of claim 17 wherein said slot is formed by a curl in containerto form said rim.
 29. The container of claim 17 wherein said slot isformed by at least two pieces of conductive material in proximity to oneanother.
 30. The container of claim 17 wherein said slot is formed by anarea of free space contained on a conductive surface.
 31. A method ofusing a slot on a container as an antenna, comprising: associating awireless communication device with a container; positioning a pluralityof feed points within a slot formed as part of said container andelectrically connected to said wireless communication device; andcommunicating monitoring information associated with the containerbetween said wireless communication device and an interrogation readerthrough a slot antenna formed by the slot within the container.
 32. Themethod of claim 31 further comprising interrogating said wirelesscommunication device at a plurality of frequencies.
 33. The method ofclaim 31 further comprising positioning a transmission line proximatesaid slot to connect electrically each of said plurality of feed pointswith said wireless communication device.
 34. The method of claim 33further comprising integrating electronic components on saidtransmission line.